1. Field of the Invention
The present invention relates to a method of forming a gate electrode in a semiconductor device, and more particularly to a method of forming a gate electrode in a semiconductor which can easily perform etching process for forming the gate electrode and reduce the resistivity of a gate electrode, when utilizing the tungsten silicide as the gate electrode material.
2. Description of the Related Art
In high integration device over 64 MDRAM, a CVD tungsten(W) silicide layer is generally used as a gate electrode material. Particularly, a dichlorsilane(DCS) tungsten silicide is widely used than a monosilan(MS) tungsten silicide as the gate electrode material considering GOI property, since the former is smaller in content of fluorine(F) impurities than the latter. However, it is difficult to apply the DCS tungsten silicide to high integration device over 1 GDRAM, because of its high resistivity.
To solve the problem, a method of forming a gate electrode of a polycide structure having a low resistivity using rapid thermal process(RTP) spike annealing, is proposed. In the method, a tungsten silicide layer of W-rich is deposited on an amorphous silicon layer. RTP spike annealing is then performed to react the amorphous silicon with the tungsten. Thereafter the tungsten silicide layer and the amorphous silicon layer are etched to form the gate electrode of the polycide structure.
However, in the method, there is problem that the amorphous silicon layer is transformed into a polysilicon layer by RTP spike annealing prior to forming the gate electrode. Furthermore, the crystal of tungsten silicide is transformed from hexagonal structure to tetragonal structure having grain of a large size during RTP spike annealing, so that the interface between the polysilicon layer and the tungsten silicide becomes inconsistent. As a result, it is difficult to perform etching for forming the gate electrode and a gate oxide layer under the gate electrode is completely removed during the etching, thereby deteriorating the reliability of a device.